The current generation of sensor devices is migrating to an integration of the sensor structure directly onto an integrated circuit die, which serves to condition and process the signals generated by the sensor. Some of these sensors, such as humidity, gas detection, and flow rate sensors, must be exposed directly to the ambient environment to take their readings. In general, the ambient environment measured by these sensors is not compatible with the materials of the integrated circuit die and may cause reliability problems if the die is exposed to this environment for an extended period.
A solution to this problem, in practice now, is to transfer mold the integrated circuit device with an epoxy resin, as is typically done for plastic-molded electronic packages. However, during the molding process, a sensor port is built into the package such that the sensor area of the die is exposed to ambient conditions, but the remainder of the die is safely encapsulated in the mold resin. A common method to form this sensor port is to use a technique known as Film-Assisted Molding (FAM).
Film-Assisted Molding incorporates a compressible film between the molding insert and the surface of the integrated die (sensor area). The film accommodates variations in the die thickness and surface topology to create a seal, preventing mold resin from bleeding into the area that must be kept clear for the sensor. Unfortunately, this film has a relatively small range of accommodation—too little compression of the film and resin will bleed under the film. Too much compression of the film, and there is a high risk that the sensor or die will incur mechanical damage, such as die cracking, embossing of the sensor surface, etc.
The current disclosure describes a method to significantly increase the range of film accommodation, thereby preventing resin bleed onto the sensor area, while eliminating mechanical damage to the sensor or die.